1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having an organic thin film.
2. Description of the Prior Art
In recent years, various studies and developments have been performed for display devices having a thin film transistor (hereinafter referred to as TFT). Since TFTs consume less electric power and can save spaces, they have been used as transistors for driving display devices for mobile equipment such as mobile telephones, notebook personal computers, and PDAs. Most portions of such TFTs are formed of inorganic semiconductor materials typically represented by crystalline silicon or amorphous silicon. The reason is that they can be manufactured by using existent manufacturing steps or manufacturing technology for semiconductor devices. However, in the case of using the semiconductor manufacturing steps, since the processing temperature upon forming a semiconductor film is as high as 350° C. or higher, there is a restriction on the substrates that can be formed. In particular, the heat resistance temperature of most of flexible materials typically represented by plastics is often 350° C. or lower and manufacture of TFTs of inorganic semiconductor materials using usual semiconductor manufacturing steps has been difficult.
For the problem described above, research and development have recently proceeded on TFT devices using organic semiconductor materials (hereinafter simply referred to as organic TFT) that can be manufactured at a low temperature. In the organic TFT, since organic semiconductor films can be formed at a low temperature, they can be formed also on substrates with low heat resistance such as plastic material. Accordingly, new flexible devices not used in the prior art can be manufactured.
For the method of forming an organic semiconductor film upon forming an organic TFT, a most suitable method has been used selectively among a printing method, for example, ink jet printing, a spin coating method, a spray method, a vapor deposition method, or dip method depending on the organic semiconductor material. For example, a low molecular weight compound such as pentacene derivative is formed into a film by the vapor deposition method, etc., and a polymeric compound such as polythiophene derivative is formed into a film from a solution. An example concerning the manufacturing method of a semiconductor device using a thin organic film transistor is disclosed, for example, in JP-A No. 2004-80026. In this example, saving the amount of the organic semiconductor material to be used has been considered by utilizing the capillary phenomenon.
Research and development have recently been performed for further reduction of the cost by manufacturing a channel portion of TFTs by a small amount of organic semiconductor material with no wasteful loss by using a printing step typically represented by ink jetting, micro-dispensing or transfer method. In addition, research and development of manufacturing also electrodes or wiring portions by printing has started.
Further, the study of a method with no positional displacement without requiring a photo-mask has started. For example, JP-A No. 2003-158134 discloses a method of using a photosensitive composition and forming a gate pattern with no positional displacement by photolithography from the rear face using source and drain electrodes as a mask.
Further, a method that does not use the photolithography for the photosensitive composition has also been studied. JP-A No. 2003-13242 is an example.